Coronavirus mutations in New York, California spark concern Mutations that have arisen in the US are spreading rapidly. Are they more contagious? And will the vaccines still be effective against them? Since health authorities have begun sequencing positive COVID-19 cases more carefully — i.e., genetically examining test results — they have also found more and more mutations. Most of those mutations are insignificant. But there are a few variants that researchers and officials are concerned about, in part because they are more contagious and because existing vaccines could be less effective at protecting against them. No more freedom of movement. Some countries are trying to stem the spread of mutations by closing borders.